1. Field of the Invention
This invention relates to a process for preparing a coated, high-surface area catalyst. More particularly, this invention relates to a method for partially wetting an inert core with a wetting agent, coating the partially wet core with a powdered hydrated form of an oxidic material or other suitable coating, drying and calcining the coated core to give a support with the desired surface area and pore structure, and finally impregnating the support with one or more solutions containing the catalytic species.
2. Description of the Prior Art
Catalysts with a high surface area (abbreviated "HSA") generally consist of active catalytic species bonded to HSA supports. These catalysts are well known and have a myriad of applications in the art. Many such applications involve reactions which are diffusion limited and which therefore require catalysts having a certain minimum particle size. To obtain sufficiently large catalyst particles, the catalytic material is sometimes applied as a coating on an inert core.
Prior art techniques generally involve the application of a HSA coating on a particle by using a slurry of the support material, which may optionally also contain the active catalytic species. For example, Stiles in U.S. Pat. No. 3,513,109 teaches a method for applying catalytic materials to a smooth support by slurrying a finely divided form of the catalytic material in a solution of a metal amine, applying the slurry to the support, then drying and calcining.
Aarons in U.S. Pat. No. 3,554,929 teaches a process for coating a smooth support with an aqueous medium of colloidal boehmite and an activated alumina composition, followed by drying and calcining. The catalytic materials of Aarons can be contained in the coating material or they may be subsequently applied by impregnating the catalyst. It is known that such colloidal sols have an inherent tendency to shrink when drying. This can cause a cracking and spalling of the coating and poor attrition resistance.
U.S. Pat. No. 3,264,228 to Burbidge describes a process for applying a slurried suspension of alumina hydrates to form a thin film coating on a support material. However, such slurry coatings also have inherent disadvantages which include non-uniform coatings and shrinking and cracking of the coating as it dries on the support. Catalytic activity may also diminish whenever the catalytic material is further treated or redispersed with liquids.
U.S. Pat. No. 3,956,377 and U.S. Pat. No. 4,077,912 to Dolhyj et al. teach the coating method of partially wetting a slightly porous inert support, tumbling the wetted support in a powder of catalytic oxides, and then drying and calcining the coated catalyst.